This invention relates to a device for testing the performance of respiratory protective devices, e.g. self-contained breathing apparatus. More particularly, this invention relates to a device for automatically performing tests on the critical functions of self-contained breathing apparatus without disassembly, with no special tools and without specially trained personnel.
Supplied air respirators are often worn by workers when exposed to highly toxic or oxygen deficient atmospheres. A self-contained breathing apparatus (SCBA) is a type of supplied air respirator. The most widely used type of SCBA supplies breathing air from a compressed air cylinder to the user.
A typical SCBA consists of the air cylinder, a first stage regulator which lowers the air pressure to approximately 120 psi, a chest mounted pressure gauge which enables the user to check his remaining air supply, a demand valve which supplies air in response to the user's inhalation, a face mask, and a warning device which alerts the user that only a fraction of his air supply is remaining.
There are many types of respiratory protective devices which utilize an airline running between a source of quality breathing air to the user.
In about 1970, a significant improvement was made in respiratory protective devices, with the introduction of positive pressure. The demand regulator was modified to continuously maintain a slight positive pressure (about 1 inch water column) in the facepiece. The idea was that all leakage would be outward from the facepiece, preventing inward leakage of contaminants.
For many years the performance of respiratory protective devices has been controlled by the U.S. Bureau of Mines, and more recently, by the National Institute for Occupational Safety and Health (NIOSH). For any respiratory protective devices to be used or sold in the United States, certain design and performance criteria must be met. These criteria include breathing resistance, and in addition for SCBA, pressure gauge accuracy, remaining service life indicator accuracy and service duration.
In order to perform the most critical of these tests, breathing resistance, an instrumented breathing machine is used. This machine consists of a test head connected to a piston assembly which functions as an artificial lung. As the piston moves in and out, exhalation and inhalation are simulated. The rate of piston movement is governed by a test curve which simulates human breathing. A pressure transducer is connected to the test head and data is recorded for all cylinder pressures.
There have been other ways to test the performance of SCBA in the field. The most common method is the use of a "regulator tester". This device measures the maximum flow which a regulator can deliver in the constant flow condition. While this and other similar tests can indicate a gross malfunction, it is not truly indicative of the performance required in actual use. Moreover, no testing devices are presently available for testing all vital functions of SCBA in a manner similar to actual use and which will give accurate and dependable results.